<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 400px;
            border: 1px solid red;
            margin-bottom: 30px;
        }
        .son{
            width: 0;
            height: 40px;
            background-color: palegreen;
            text-align: center;
            line-height: 40px;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="son">
            <span>0</span><span>%</span>
        </div>
    </div>
    <button id="btn">安装</button>
    <script>
        let btn = document.getElementById("btn")
        let div = document.getElementsByTagName("div")
        let span = document.getElementsByTagName("span")
        let timer = null
        btn.onclick = function(){
            let num = 0
            if(timer == null){
                let timer = setInterval(()=>{
                    num+=1
                    div[1].style.width = num+"px"
                    span[0].innerText = Math.ceil(num/400*100)
                    if(num == 400){
                        clearInterval(timer)
                    }
                },10)
            }
        }
    </script>
</body>
</html>